In certain 4-wheel drive automobiles, they can selectively switch front wheels or rear wheels to driving wheels or driven wheels using a clutch function provided with a wheel bearing apparatus. Such a wheel bearing apparatus 50, with the clutch function, is shown in FIG. 11. A wheel hub 52 is axially mounted on an axle 51 of a drive train. A double row tapered roller bearing 53 is a rolling bearing mounted on the wheel hub 52 at its axially center portion. A coupler ring 54 is arranged axially by the side of the double row tapered roller bearing 53. In addition, the wheel bearing apparatus 50 is coaxially supported on the axle 51, via a deep groove ball bearing 55 and a needle bearing 56 arranged between the axle 51 and the wheel hub 52. A reference character “G” denotes a slidable gear ring.
The wheel hub 52 has a cylindrical portion 57 formed coaxially with the axle 51. A flange 58 radially extends from the cylindrical portion 57 near the outer-side end. A caulked portion 59 is formed by bending an inner-side end of the cylindrical portion 57 radially outward. A splined portion 60 has a plurality of spline recesses (spline grooves) 60a and a plurality of spline projections 60b alternately arranged with each other on the outer circumference of the cylindrical portion 57 near the caulked portion 59. The splined portion 60 is mated with an inner circumferential splined portion 61 formed on the inner circumference of the coupler ring 54. The flange 58 is formed with a plurality of through apertures 58a. Fastening members B0, such as bolts, are inserted into the apertures 58a to fasten a wheel (not shown).
The double row tapered roller bearing 53 has an inner ring 62 and an outer ring 63. Double row tapered rollers 64, 65 are arranged side by side in an axial direction between the inner ring 62 and the outer ring 63.
In more detail, the inner ring 62 has a first inner ring member 66 with a first raceway surface 66a. A second inner ring member 67 has a second raceway surface 67a. The first inner ring member 66 and the second inner ring member 67 are arranged so that they abut each other. An outer-side end face 66b abuts against a root portion of the flange 58 of the wheel hub 52. An inner-side end face 67b of the second inner ring member 67 abuts against an end face of the coupler ring 54. Accordingly, the coupler ring 54 and the inner ring 62 (first and second inner ring members 66, 67), forming the double row tapered roller bearing 53, are firmly secured so as not to be rotated relative to the wheel hub 52.
The outer ring 63 has a first raceway surface 63a, a second raceway surface 63b, and a flange portion 63c, extending radially outward. The flange portion 63c is adapted to be secured to a steering knuckle (suspension apparatus) of a vehicle. A numeral 68 denotes a sealing member.
The coupler ring 54 has a generally annular configuration and is axially arranged side by side with the second inner member 67. Thus, it abuts against the end face 67b of the second inner ring member 67. The outer circumference of the coupler ring 54 is formed with a plurality of spline recesses (spline grooves) 69a and a plurality of spline projections 69b, forming an outer circumferential splined portion 69. The outer circumferential splined portion 69 is adapted to be mated with a splined portion G1 of a gear ring G.
As shown in FIG. 12, the inner-side inner circumferential edge of the spline projection 61b, of the inner circumferential splined portion 61 of the coupler ring 54, is chamfered to form an inner-side chamfered portion 70, with a curved surface. The chamfered portion 70 is designed to be positioned inner-side of the splined portion 60 of the wheel hub 52. In particular, it is designed so that a distance L is smaller than a distance X. The distance L is a distance from the inner-side end face 71 of the coupler ring 54 to the outer-side end 71a of the chamfered portion 70. The distance X is a distance from the inner-side end face 71 of the coupler ring 54 to the end point 60c of the spline recess 60a of the splined portion 60 of the wheel hub 52. Thus, it is possible to increase the bending radius of the caulked portion 59, formed on the inner-side end of the cylindrical portion of the wheel hub 52, and accordingly effectively suppress the generation of cracks in the root of the caulked portion 59 (e.g., see Japanese Patent Publication No. 4466302).
In the prior art technology, a “V”-shaped configuration (shown by a dotted line in FIG. 12) is often caused at the root of the caulked portion 59 during the performing of the actual caulking machining. As a result, the deforming stress would be concentrated in the “V”-shaped portion of the caulked portion 59. Thus, the caulking strength would also be reduced.